Computer systems have been indispensable basic living tools for modern people. They have been developed for almost seventy years, and are developed especially rapidly in recent ten years. Nowadays, because of their powerful functions, the power consumption of computer systems increases as well. Accordingly, the power management of computer systems is an important index of computer system development. In order to enhance power usage efficiency of computer systems, Microsoft Corporation has ever developed the Advanced Power Management (APM) to enhance power usage efficiency. However, because the APM does not execute power management actions according to a user's usage state, the purpose of using power efficiently cannot be achieved. In consideration of the concern, three major computer system providers, including Intel, Microsoft, and Toshiba, collaboratively laid down the ACPI as a standard for power management. The ACPI employs operation systems of computer systems to perform power management of computers.
Because a user controls a computer system by means of an operating system, the operating system can perform more efficient power management according to the user's usage state, and the user can employ the operating system to achieve usage convenience by adjusting the ACPI directly as well. The function states of the ACPI include global system states (G), device states (D), sleeping states (S), and CPU states (C).
Owing to the demanding requirements by people for the functions of a computer system, the traditional deployment of a CPU applying single host bridge cannot enhance functions of the computer system. Thereby, currently the direction of development for the majority of computer systems aims at the application of a plurality of host bridges by a CPU. However, a CPU provided with a plurality of host bridges cannot enter the C3 state of the CPU state of the ACPI, because before making the CPU enter the C3 state, it is necessary to stop the host bridges from transmitting bus master signals to the CPU when the host bridges are receiving the bus master signals. Nevertheless, because a computer system can only transmit a command to a host bridge, the other host bridges cannot receive the command. As a result, when the CPU enters the C3 state, the other host bridges still transmit the bus master signals to the CPU as they receive the bus master signals, which will cause problems.
Consequently, at present, a computer system whose CPU is provided with a plurality of host bridges doesn't support its CPU to enter the C3 state, which prevents the CPU from providing perfect power management capability. Because the C3 state is the most power-saving state of a CPU, the CPU cannot enter the most efficient sleeping state even though it is in the idle time, which will result in consumption of power. This problem is particularly important for portable computers because it will consume the power of batteries, and thus lowers the usage performance of the portable computers.
The present invention provides a method of power management of a CPU connecting with a plurality of host bridges aimed to solve the problem as describe above. The method not only can improve the drawback of rapid power consumption due to inability to enter the C3 state of a CPU, but also can further reduce the charging frequency required by batteries of portable computers, and thereby increase the battery life.